The Centre for Environment, Fisheries and Aquaculture Science (Cefas) is an Executive Agency of the Department of Environment, Food and Rural Affairs (Defra), formerly the Ministry of Agriculture, Fisheries and Food (MAFF). It was also known previously as the Directorate of Fisheries Research (DFR). This data policy refers to data collected by the organisation under all titles.

These data have no specific confidentiality restrictions for academic users. However data are restricted for commercial requests and clearance must be obtained by BODC from Cefas before they are released.

Users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgement.

The recommended acknowledgement is: "This study uses data from the Centre for Environment, Fisheries and Aquaculture Science (Cefas), provided by the British Oceanographic Data Centre."

Guildline 8705 CTD

The 8705 CTD is a conductivity-temperature-pressure profiler designed for marine applications down to depths of 6000 m. The instrument includes an anodised aluminium tube with a steel cage to protect the temperature and conductivity sensors and a urethane cap to protect the pressure sensor.

Specifications

Parameter

Range

Accuracy

Resolution

Stability

Response time

Pressure

0 to 6000 dbar

± 0.15% of full range

± 0.01% of full range

-

< 50 ms

Temperature

-2 to 30 °C

± 0.005 °C

± 0.0005 °C

± 0.002 °C over 30 days

± 0.0025°C over 6 months

< 50 ms

Conductivity *

100 ppm to 40 ppt

± 0.005 ppt

± 0.001 ppt

± 0.002 ppt over 6 months

< 50 ms

* Conductivity specifications are given in terms of equivalent salinity

RV Corystes Cruise 1/92 CTD Data Documentation

Instrumentation

The CTD used was S/N 45056. The transmissometer used during the cruise was S/N 479, with a 5 cm path.

Sampling Protocol

Eighty-two CTD profiles were obtained during the cruise. Reversing thermometers were fitted to the Niskin used to collect samples from close to the seabed. Samples for salinity analysis were collected from both near the surface and close to the seabed.

Calibration

Not all the calibration data collected were used to calibrate the CTD sensors for the following reasons:

Thermometer differences too large (>0.02).

It was clear from the profiles obtained at the time of station that some T and/or S values measured by the CTD were variable, believed real, not an instrument malfunction, and unsuitable for calibration use. Eighteen data sampling points were not used because of this.

Pressure

The pressure sensor was corrected using the laboratory calibration of September 1991 at T = 12 °C.

P(cor) = P(ctd) - 1.6

Normally this is checked by comparing CTD pressure with that derived from water depth and altimeter height, but a fault with the altimeter throughout this cruise made this impractical.

Temperature

The temperature sensor was corrected using laboratory calibration of December 1991.

T(cor) = T(ctd) + dT

dT = a*T(ctd)*T(ctd) + b*T(ctd) + c

where:

a = -2.59480e-6 b = -1.60314e-4 c = 3.128e-3

These coefficients are equivalent to a correction of approximately 2 mK for the range of temperatures encountered during the cruise.

A comparison between thermometer and uncorrected CTD temperatures is shown in Fig. 1. If it is assumed that the thermometer temperatures are accurate to 0.02 °C and the CTD to 0.01 °C then all differences to within 0.03 °C are acceptable. Only four out of sixty-nine values are outside this range and the mean difference is 0.002 °C.

Salinity

One hundred and forty two salinity samples were used to calibrate the conductivity sensor.

CR(cor) = CR(ctd)*[ a*T(cor) + b*P(cor) + c ]

where:

a = -1.467061e-5 b = 2.790880e-6 c = 0.999653

The rms difference between salinometer and corrected CTD salinity was 0.018.

Fig. 2 shows how effective these coefficients are in correcting the CTD salinity estimates for the calibration samples. Note that the CTD salinity of the upper histogram was derived after the CTD temperature and pressure had been corrected but prior to applying corrections to the CTD conductivity ratio. The Figure gives an indication of how well the CTD conductivity is corrected.

Fig. 3 displays the spread in the ratio of conductivity-ratio of the CTD to that of the water samples prior to applying the correction.

Fig. 4 shows the difference between the water sample salinity and the uncorrected CTD equivalent before any of the CTD sensors are corrected; the CTD is generally 0.02 too high.

Fig. 5 shows the difference between the water sample salinity and the corrected CTD equivalent after all three sensors (pressure, temperature and conductivity ratio) have been corrected.

Stations 23 to 45 are at or near the entrance to the Humber Estuary, stations 62 to 74 are well into the Wash whilst station 80 is at the outer Thames Estuary. The differences are relatively larger at these stations.

If the CTD is assumed to have an accuracy of 0.01 in terms of salinity and the salinometer of 0.006 then the corrected CTD salinity values should lie within 0.016. In this instance 28 out of 142 samples (20%) fall outside this range (see Fig. 2). If the data from the above stations are removed from the calibration this figure is reduced to 6 from 85 (7%) and the rms difference between corrected CTD and water sample salinity is 0.011; 7 from 85 lie outside ±0.013.

Suspended Load

The suspended load estimates from %transmission were calculated from the following:

suspended load (mg/litre) = B * ln (%transmission) + C

station number

B

C

1 to 21

-54.5

215.8

23 to 36

-69.0

263.8

37 to 48

-55.0

217.6

49 to 74

-52.1

205.0

77 to 83

-103.0

397.4

84 to 99

-79.1

309.1

These coefficients derived from suspended load measurements on samples collected whilst transmission being logged, two samples per station.

General Data Screening carried out by BODC

BODC screen both the series header qualifying information and the parameter values in the data cycles themselves.

Header information is inspected for:

Irregularities such as unfeasible values

Inconsistencies between related information, for example:

Times for instrument deployment and for start/end of data series

Length of record and the number of data cycles/cycle interval

Parameters expected and the parameters actually present in the data cycles

Originator's comments on meter/mooring performance and data quality

Documents are written by BODC highlighting irregularities which cannot be resolved.

Data cycles are inspected using time or depth series plots of all parameters. Currents are additionally inspected using vector scatter plots and time series plots of North and East velocity components. These presentations undergo intrinsic and extrinsic screening to detect infeasible values within the data cycles themselves and inconsistencies as seen when comparing characteristics of adjacent data sets displaced with respect to depth, position or time. Values suspected of being of non-oceanographic origin may be tagged with the BODC flag denoting suspect value; the data values will not be altered.

The following types of irregularity, each relying on visual detection in the plot, are amongst those which may be flagged as suspect:

If a large percentage of the data is affected by irregularities then a Problem Report will be written rather than flagging the individual suspect values. Problem Reports are also used to highlight irregularities seen in the graphical data presentations.

Inconsistencies between the characteristics of the data set and those of its neighbours are sought and, where necessary, documented. This covers inconsistencies such as the following:

Maximum and minimum values of parameters (spikes excluded).

The occurrence of meteorological events.

This intrinsic and extrinsic screening of the parameter values seeks to confirm the qualifying information and the source laboratory's comments on the series. In screening and collating information, every care is taken to ensure that errors of BODC making are not introduced.

Joint Nutrient Study I (JoNuS)

Concerns by the scientific community about the impact of nutrient inputs to the sea; a lack of information on inputs from the UK and on the spatial and temporal distribution and cycling of nutrients in UK waters provided the impetus for the JoNuS project.

The project sought to quantify the input of nitrogen, phosphorus and silicon from UK estuaries to the North Sea through a good understanding of the estuarine processes that control the flow of these nutrients. It focussed on the Great Ouse/Wash and the Humber outflows. Its specific objectives were:

To measure the fluxes of nutrient elements (N, P, Si) through selected major estuaries on a quantitative annual basis in order to determine the net input to the sea resulting from gross river inputs.

To quantify the processes controlling the fluxes of nutrients through estuaries.

The Centre for Environment, Fisheries and Aquaculture Science (CEFAS) hosted the project, which involved scientists from CEFAS, the University of East Anglia, the University of Essex, the Plymouth Marine Laboratory and the National Rivers Authority (now the Environment Agency). It was funded by the then Ministry of Agriculture, Fisheries and Food (MAFF) and the Department of Environment, now the Department of Environment, Food and Rural Affairs (Defra).

The project ran from April 1990 to March 1995, with marine field data collection between May 1990 and December 1993. Data collection involved ship based surveys which were complemented by estuarine transects and specific process studies.

Initially, the surveys were on a quarterly basis up to October 1992, however monthly surveys were carried out during 1993. During this intensive survey period, the programme focused on the Great Ouse/Wash; with a continuing, but lower level, of activity devoted to the Humber. An additional multi-project cruise, carried out in January 1995, also complemented the JoNuS data set. Further details of the JoNuS I cruises are provided below: